1. Field of the Invention
This Invention relates to hardware designed into silicon circuitry which prevents the circuitry from being forced to operate outside of predetermined parameters. More specifically, the present invention relates to hardware circuitry which may detect over or under voltage conditions, high- or low-speed clocks, and over or under temperature conditions. The circuitry may reset or shut down the silicon circuitry in response to such detections.
2. Description of Related Art
Microcontrollers have become commonplace in today's society. Over time microcontrollers have accommodated and provided a wide variety of solutions to various problems in the electronic and automation industries. At present, microcontrollers are beginning to be placed in devices or used as devices that perform secure transfers of money, monetary equivalents and secure information.
As a result of using microcontrollers for transferring and handling secure information and data, there are people dedicated to "breaking the code" or mathematically evaluating the secure data transfers in order to determine the secrets and proprietary techniques of the secure data transfers.
Smart cards, for example, have been "attacked" by varying the frequency to the microprocessor and the coprocessor at specific times. The frequency can be increased to produce race conditions in the integrated circuit that will make the circuit operate improperly due to the limited time between rising and falling edges of the clock signal. Calculation errors may result. A calculation error resulting from such a race condition can be compared with a similar calculation made with a good/correct result to correspondingly resolve the secret key(s) associated with the calculation and thereby defeat the security of the integrated circuit.
In the area of cryptography, an important article was written entitled "On the Importance of Checking Cryptographic Protocols for Faults", Dan Boneh, Richard A. DeMillo, Richard J. Lipton, Security and Cryptography Research Group, Bellcore, 1997(hereinafter "the Bellcore article"). The Bellcore article discusses attack techniques targeted at RSA encryption and Rabin signatures. In essence the Bellcore article indicates that from time to time hardware which performs RSA encryption calculations may introduce errors. If the errors are found or can be forced by an attacker, then the RSA code may be broken by using various algorithms. Thus, there is a need for integrated circuits which perform encryption calculations that have means for stopping or limiting the circuitry from being stressed into introducing errors into calculations.